Tiresias serpentes duos concumbentes vidit, quos cum virga percussisset, in feminam conversus est. Iterum post temporis seriem eos concumbentes vidit, similiterque percussis iterum est in pristinam naturam conversus.
--Fulgentius, Myth. II.8
When Tiresias saw two snakes mating, he struck them with a stick and was turned into a woman. After a while, he saw them mating again, and as soon as he struck them again he returned to his original body (in pristinam naturam).